Composites of particulate and polymers using a variety of both high and low density particulate materials have been made. Polymers have been combined with fillers and certain particulate materials at various loadings. Such materials have a broad spectrum of applications and uses in both consumer and industrial applications. Such applications include composites with density less than the density of the polymer phase and with very high density.
In one application high density is a goal. Lead has been commonly used in applications requiring a high density material. Applications of high density materials include shotgun pellets, other ballistic projectiles, fishing lures, fishing weights, wheel weights and other high density applications. Lead has also been used in applications requiring properties other than density including in radiation shielding because of its resistance to EMI and malleability characteristics. Press-on fishing weights made of lead allow the user to easily pinch the weight onto a fishing line without tools or great difficulty. In the case of shotgun pellets, or other ballistic projectiles, lead offers the required density, penetrating force and malleability to achieve great accuracy and minimum gun barrel wear. Lead has been a primary choice of both hunting and military applications. Many jurisdictions in the United States and elsewhere have seriously considered bans on the sale and use of lead shot and lead sinkers due to increasing concentrations of lead in lakes and resulting mortality in natural populations. Other high-density materials such as depleted uranium have been proposed and implemented. Composite materials have been suggested as a replacement for lead and other high-density materials. Composite materials have been made for many years by combining generally two dissimilar materials to obtain beneficial properties from both. A true composite is unique because the interaction of the materials provides the best properties of both components.
Again, filled polymeric materials have been produced for many years but have been limited in the degree of fill that can be attained due to the undesirable decrease in the physical properties of the composite product at high volumetric loadings of particulate in polymer.
Many types of composite materials are known and are not simple admixtures. Generally, the art recognizes that combining metals of certain types and at proportions that form an alloy provides unique properties in metal/metal alloy materials. Metal/ceramic composites have been made typically involving combining metal particulate or fiber with clay materials that can be fired into a metal/ceramic composite. Tarlow, U.S. Pat. No. 3,895,143, teaches a sheet material comprising elastomer latex that includes dispersed inorganic fibers and finely divided metallic particles. Bruner et al., U.S. Pat. No. 2,748,099, teach a nylon material containing copper, aluminum or graphite for the purpose of modifying the thermal or electrical properties of the material, but not the density of the admixture. Sandbank, U.S. Pat. No. 5,548,125, teaches a clothing article comprising a flexible polymer with a relatively small volume percent of tungsten for the purpose of obtaining radiation shielding. Belanger et al., U.S. Pat. No. 5,237,930, disclose practice ammunition containing copper powder and a thermoplastic polymer, typically a nylon material. Epson Corporation, JP 63-273664 A shows a polyamide containing metal silicate glass fiber, tight knit whiskers and other materials as a metal containing composite. Bray et al., U.S. Pat. Nos. 6,048,379 and 6,517,774, disclose an attempt to produce tungsten polymer composite materials. The patent disclosures combine tungsten powder having a particle size less than 10 microns, optionally with other components and a polymer or a metal fiber. The materials sold by the Bray et al. assignee and the materials disclosed in the patent do not attain a density greater than 10.0 gm-cm−3. Barbour et al., U.S. Pat. No. 6,411,248, discloses using a glue-gun applied hot-melt radar-absorbing material, including carbonyl iron powder in thermoplastic polyurethane and a unique metal deactivator in amounts useful for a specific application.
A high density thermoplastic metal composite material has not been obtained that can be used to form objects using hot melt technology apart from compounder and extruder technology. A substantial need exists for a formable material that has high density, low toxicity, and improved properties in terms of electrical/magnetic properties, malleability, thermal processability, particularly using existing thermal processing equipment, and viscoelastic properties that can be used in simple hot melt applicator devices. Such materials are suited for consumer applications, small batch processes, semi-works manufacturing and other applications involving the efficient application of amounts of the composites using hand operated equipment.
Low density melt molding formulations can be produced via the use of low density materials including for example: hollow glass spheres. Hollow glass spheres are widely used in industry as additives to polymeric compounds, e.g., as modifiers, enhancers, rigidifiers and fillers. These spheres are strong enough to avoid being crushed or broken during further processing of the polymeric compound, such as by high pressure spraying, kneading, extrusion or injection molding. Proper distribution of the glass spheres is completed by maintaining appropriate viscosity of the polymer/glass sphere formulation. Furthermore, it is desirable that these spheres be resistant to leaching or other chemical interaction with their associated polymeric compound. The method of expanding solid glass particles into hollow glass spheres by heating is well known. See e.g., U.S. Pat. No. 3,365,315. Glass is ground to particulate form and then heated to cause the particles to become plastic and for gaseous material within the glass to act as a blowing agent to cause the particles to expand. During heating and expansion, the particles are maintained in a suspended state either by directing gas currents under them or allowing them to fall freely through a heating zone. Sulfur, or compounds of oxygen and sulfur, serves as the principal blowing agent.
A number of factors affect the density, size, strength, chemical durability and yield (the percentage by weight or volume of heated particles that become hollow) of hollow glass spheres. These factors include the chemical composition of the glass; the sizes of the particles fed into the furnace; the temperature and duration of heating the particles; and the chemical atmosphere (e.g., oxidizing or reducing) to which the particles are exposed during heating.
There have been problems in attempting to improve the quality and yield of hollow glass spheres. One reason is that it was believed that the percentage of silica (SiO2) in glass used to form hollow glass spheres should be between 65 and 85 percent by weight and that a weight percentage of SiO.sub.2 below 60 to 65 percent would drastically reduce the yield of the hollow spheres.
Hollow glass spheres have average densities of about 0.1 grams-cm−3 to approximately 0.6 grams-cm−3 or about 0.12 grams-cm−3 to approximately 0.6 grams-cm−3 and are prepared by heating solid glass particles. For a product of hollow glass spheres having a particular desired average density, there is an optimum sphere range of sizes of particles making up that product which produces the maximum average strength. This range can be expressed by >10 to 250 μm.
Glass spheres used commercially can include both solid and hollow glass spheres. All the particles heated in the furnace do not expand, and most hollow glass-sphere products are sold without separating the hollow from the solid spheres.